Heat the butter in a large, heavy-based saucepan over medium heat, add the finely sliced onion and fry gently for about 5 minutes, stirring.
Add the pumpkin and let it cook for a few minutes, stirring occasionally.
Add some stock, if needed.
Season lightly with salt.
Turn up the heat, add into the rice and fry it for one minute until the grains become shiny, stirring continuously.
Pour into the wine and let it evaporate.
Next, reduce the heat and cook the risotto adding the warm stock a little at a little, stirring, and allowing the rice to absorb it before adding more.
Continue until the risotto is ready (this will take more or less 16/18 minutes, it depends on the kind of rice).